1. Field of the Invention
The present invention relates to a semiconductor device and a method of driving the semiconductor device.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electrooptic device, a semiconductor circuit, and an electronic device are all semiconductor devices.
The present invention relates to an object, a method, or a manufacturing method. Further, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor layer, a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a driving method thereof, or a manufacturing method thereof. In particular, the present invention relates to a semiconductor device including a transistor, a display device, a light-emitting device, or a driving method thereof, for example. Further, the present invention relates to, for example, an electronic device including the semiconductor device, the display device, or the light-emitting device.
2. Description of the Related Art
Signal processing units such as central processing units (CPUs) vary in structure depending on the intended use. Examples of components of a signal processing unit are a logic circuit performing arithmetic processing, a main memory for storing data or a program, a register or a cache memory which temporarily holds data for carrying out arithmetic processing or holding a program execution state, for example, and the like.
In a signal processing unit, a logic circuit performing arithmetic processing does not constantly operate and stops operation at many periods. Power gating is a known technique which attempts at a reduction in electric power by interrupting power supply to a circuit that stops operation at such periods (e.g., see Patent Document 1).